The present invention relates to a resin composition which shows especially excellent balance of mechanical properties including mainly rigidity and is superior in processability, oil resistance and chemical resistance.
More particularly, it relates to a resin composition for injection molding, extrusion molding or blow molding which comprises a polyolefin, especially, a crystalline polyolefin, a polyphenylene ether resin, a partially hydrogenated alkenyl aromatic compound-isoprene block copolymer and an ethylene-.alpha.-olefin copolymer elastomer and is excellent in balance of mechanical properties including rigidity and heat resistance and superior in processability, organic solvent resistance and chemical resistance.
Polyolefins are superior in processability, toughness, water resistance, organic solvent resistance, chemical resistance, etc., low in specific gravity and inexpensive and hence have been widely used for production of various shaped articles and sheets. However, they suffer from the problem in heat resistance, which has hindered development of new uses thereof.
On the other hand, polyphenylene ether resins have excellent heat resistance, but has difficulties in processability and solvent resistance, which impose limitation on the scope of application. For improvement of processability and impact strength, blend of polyphenylene ether resin with a styrene resin is utilized, but this has defect in solvent resistance and is limited in scope of application. For example, the blend is not suitable in the field which requires resistance to oily solvents such as gasoline.
In an attempt to utilize the respective merits of these polyolefin and polyphenylene ether and offset their defects, various blend compositions have been proposed. For example, a composition has been proposed for improvement of processability and tensile strength (Japanese Patent Kokoku No. 42-7069). However, this composition does not necessarily suffice the relatively high level of mechanical strength which is required in industrial fields. Furthermore, for improving compatibility between polyolefin and polyphenylene ether resin to enhance mechanical strength, for example, a composition to which a styrene-butadiene block copolymer or its hydrogenated product is added (Japanese Pat. Kokai Nos. 53-71158, 54-88960 and 59-100159) and the above composition to which inorganic filler is added (Japanese Patent Kokai No. 58-103556) have been proposed. According to these proposals, processability and mechanical strength can be improved, but the organic solvent resistance possessed by polyolefin cannot be sufficiently exhibited for the reasons that amount of polyolefin added is small or matrix (continuous phase) comprises polyphenylene ether resin or composition of polyphenylene ether resin and styrene resin and the like. Moreover, there has been proposed a composition which comprises polyphenylene ether and a large amount (more than 20% by weight) of polyolefin to which are further added a diblock copolymer or radial teleblock copolymer composed of alkenyl aromatic compound and conjugated diene or hydrogenated polymers thereof as a compatibilizing agent (Japanese Patent Kokai Nos. 58-103557 and 60-76547). That is, it is said that a blend of a low-density polyethylene as polyolefin and polyphenylene ether resin has been improved in compatibility and can be improved in tensile characteristics and fragility by the addition of hydrogenated product of alkenyl aromatic compound - conjugated diene block copolymer. However, improvement only in compatibility is not enough to satisfy various properties required for common resins. For example, the composition disclosed in Japanese Patent Kokai No. 60-76547, namely, a resin composition comprising the three components of a polyphenylene ether, a low-density polyethylene as polyolefin, a component of large amount, and a hdyrogenated product of alkenyl aroamtic compound-conjugated diene block copolymer as a compatibilizing agent for the former two components has limitation in its use owing to its very low rigidity level. Among the above-mentioned combinations, resin compositions which contain polypropylene as polyolefin are somewhat improved in rigidity and heat reistance, but these are still not enough in practical use and further improvement has been desired.
The inventors have conducted intensive research in an attempt to make further improvement and to provide resin compositions which can satisfy balance of mechanical strength of relatively high level and solvent resistance and processability of relatively high level which are required in various uses such as fields of industrial parts.
As a result of investigation conducted by the inventors on polyphenylene ether resin, polyolefin and various additives, it has been found that a resin composition which shows excellent balance of mechanical properties and is superior in solvent resistance and processability can be obtained by adding a relatively small amount of a hydrogenated product of alkenyl aromatic compound-conjugated diene block copolymer having a specific structure and an ethylene-.alpha.-olefin copolymer elastomer to combiantion of polyphenylene ether resin and polyolefin, preferably crystalline polyolefin. Thus, the present invention has been accomplished.